1. Field of the Invention
The present invention relates to fans of the type driven by brushless electric motors, particularly for use in motor vehicle engine cooling systems. In particular, the present invention relates to such fans having motor cooling features.
2. Description of the Related Art
Conventional electric motors may be generally characterized by a cylindrical housing which contains the various stationary and rotating components of the motor, as well as the associated electronic circuitry. In general, the housing is regarded as a combination of the rotor and a rear cover member. Such motors are generally utilized to drive a cooling fan in automotive applications wherein the motor is of the brushless-type and the fan is attached to a fan hub which is in turn attached to the rotor of the motor.
In general, the motor components are arranged in a relatively small space within the motor housing, thus resulting in the production of significant amounts of heat with little dissipation. In order to dissipate the heat, a cooling air path extends through the housing and a cooling device known in the art as a heat sink is provided with heat dissipating fins within the housing. In operation, the atmospheric air passes through the housing past the components and the fins of the heat sink and thereby cools the motor.
It has been found that the provision of a cooling air path through the motor housing is not always sufficient to produce the requisite cooling, particularly when the motor is used to rotatably drive a fan of considerable weight. In particular, the fan may contain any of a number of fan blades, generally between four and ten. In such instances, there is relatively substantial power consumption and significant amounts of heat generation within the brushless motor, which makes it desirable to provide additional cooling enhancement for the brushless motor. In this regard several alternatives may be considered, including increasing the spaces between the motor components, or increasing the cooling air flow through the motor, for example. In view of limited space requirements the first mentioned alternative is not viable.
U.S. Pat. No. 4,838,760 relates to a fan with motor cooling enhancement in which a plurality of arcuately shaped webs are provided on a fan hub for inducing the flow through the motor and through a plurality of openings formed in an axially extending wall of the hub. This arrangement utilizes additional energy to force the airflow, while its relatively complicated structure increases manufacturing costs. U.S. Pat. No. 5,217,353 relates to a fan for motor vehicles wherein a motor includes a casing having a stationary part with holes for taking in air from outside for ventilating the interior of the motor and a rotary part with holes which act as outlet ducts for the internal ventilation air. The cross-sections of the ducts decrease in the direction of the air-flow and open into the outside atmosphere in regions over which the air-flow induced by the fan wheel passes in operation.
Although the attempts to enhance air cooling of such motors have been effective to a limited extent, in general they have not achieved a level of volumetric air-flow and a satisfactory degree of cooling which is necessary to maintain the predetermined desired temperatures of such air cooled motors, particularly those of the brushless type. We have invented a fan assembly intended to be driven by such type of motor, wherein the actual fan assembly includes structure which enhances the flow of cooling air through a cooling air path extending through the motor and thereby provides for cooling of the motor by which it is rotatably driven.